(1) Field of the Invention
The present invention relates to an ignition timing control unit for a motor vehicle or car engine, more particularly to an engine ignition timing control unit for a car, which controls an output timing for the ignition current to be sent to a spark plug by suitably correcting the spark advance angle in accordance with the averaging value of the engine speed and a method for controlling the ignition timing.
(2) Description of the Prior Art
In a large displacement manual transmission car, since the variation in the torque due to the manipulation of an accelerator is large, there were resulting problems of backlash in gears in a drive system or gears of a rotating portion of detecting means for engine speed or twisting of a propeller shaft becomes large when performing a rapid acceleration or deceleration, or shocks of the car due to deformation of a tire or tires thereof become large as well as transient vibrations of the car forward and backward, i.e. the known phenomena that the car exhibits repeated knocking vibrations (which phenomena is referred to hereinafter as a "hiccup phenomena") forward and backward as either the acceleration or deceleration operation performed becomes large, thus degradating the drivability.
Moreover, in a middle or small displacement engine manual transmission car as well, similar problems as described above have occurred of late, as the high output tendency of engines progresses, and, in addition, as a result of the provision of a lock-up mechanism to an automatic transmission car, which has been developed recently, the similar problems as those in the manual transmission car have occurred. For instance, in the case where the "hiccup phenomena" as described in the foregoing occurs, the engine speed, the value of spark advance angle (i.e. effective advance angle value) and the car speed before or after acceleration to the time elapsed become the ones as indicated by the dotted lines in FIGS. 5(a), (b) and (c) or in FIGS. 7(a), (b) and (c).
In order to overcome the above problems and drawbacks, a car having an ignition timing control unit has been proposed in which the leading edge of the transmission torque for transmitting the engine output to drive wheels of the car can be smoothed when the car speed is abruptly changed by making the ignition timing to be either advance angle or delay angle in accordance with the fluctuation or change in the engine speed, thus improving the drivability.
Since, however, a process for averaging the engine speed (which will be described later) is not carried out in the above ignition timing control unit according to the prior art, an excessive control is often carried out by the change in gears of a rotating portion of detecting means for detecting the engine speed or the backlash in the gears of a drive system, thus causing a problem that the ignition timing cannot be necessarily controlled accurately.